Use of polyester resins for the production of articles having good properties as barriers to water vapor

ABSTRACT

Polyester resins formed by recurring units X=[O—(CH 2 ) n —OCO—(CH 2 ) m —CO] and/or Y=[O—(CH 2 ) k —CO], where the half-sum of n+m is equal to or greater than 6 and k is a number equal to or greater than 6, or by copolymers comprising units and/or sequences having the formula x i [O—(CH 2 ) ni —OCO—(CH 2 ) mi —CO]; y j [O—(CH 2 ) kj —CO] where: i,j=1-5; n i =2-22; m i =0-20; k j =1=21; (Formula (1)) and x i  and y j  vary between 0 and 1 and are molar fractions of the various units such that (Formula (2)), are used for the preparation of products in which a permeability to water vapour of less than 350 g×30 μm/m 2  per day, measured at 38° C. and 90% RH and good biodegradability are required.                    ∑     i   =   1     5          x   i       +       ∑     j   =   1     5          y   j         =   1           (   1   )                     ∑     i   =   1     5            x   i     ·     (         n   i     +     m   i       2     )         +       ∑     j   =   1     5            y   j     ·     k   j           ≥   6           (   2   )

The present invention relates to the use of biodegradable polyesterresins in the production of formed articles having good properties asbarriers to water vapour.

The water-vapour barrier properties of biodegradable polymers developedin recent years are quite poor.

For example, polyesters such as polyhydroxybutyrate-valerate, polylacticacid, polyglycolic acid, polycaprolactone, polybutylene succinate,copolymers such as polybutylene adipate-co-terephthalate,polyester-amides such as polybutylene adipate-co-caprolactam, polyvinylalcohol, ethylene-vinyl alcohol copolymers, polyesters-urethanes, andesters of cellulose and regenerated cellulose have permeabilities towater vapour greater than 300 g×30 μm/m² per day at 38° C. and 90%relative humidity (RH) (Lyssy method).

The poor barrier properties can be related to the fact that thesepolymers have good biodegradability which, in order for the bacterialaction to be performed advantageously, means that the polymer should bewettable and hence contains polar groups in its structure with aconsequent reduction in its water-vapour barrier properties since thepolar groups increase the solubility of water in the polymer and henceits permeability to water vapour.

High permeability to water vapour considerably limits the fields of useof biodegradable polymers such as the above-mentioned aliphaticpolyesters or copolyesters, particularly where good biodegradability andlow permeability to water would be very desirable.

Fields of use in which there is a particular need for biodegradablematerials having good water-vapour barrier properties are, for example,the hygiene field (so-called non-breathable nappies, that is to say,nappies with a low transpiration value, similar to the nappies which arein use with a backsheet of polyethylene and non-woven polypropylenefabric), multi-layer and non-multi-layer food packaging based onlaminated milk cartons, mulching of soils where the evaporation of waterthrough materials is to be as limited as possible, containers for soilfor growing plants in greenhouses, sacks for collecting grass cuttingswhich require reduced biodegradation rates by virtue of a lowerwettability of the biodegradable film of which the sack is made,non-woven, fabric which can provide a dry feel for nappies, fishing netswhich must not undergo significant alterations due to water during theperiod of use, expanded products for packaging which requires moistureprotection whilst remaining biodegradable, irrigation pipes foragriculture, products in contact with liquid foodstuffs, such asfast-food cups, plates and drinking straws, expanded trays forfoodstuffs, blister packs for pharmaceutical products, nurseryplant-pots through which moisture must not be able to pass and whichmust have a degradation process which does not interfere with the growthof the plants, hygiene products such as colostomy bags and the like, orblood containers, fibres for disposable products which can withstandwater and a few washings, for disposable hosiery and garments, etc.

It has now been found, unexpectedly—in view of the outstandingpermeability of aliphatic polyesters such as polybutylene adipate,polybutylene succinate, polyhexamethylene adipate and polybutyleneadipate-co-terephthalate to water vapour—that the polyester resinsdefined below have good water-vapour barrier properties and, at the sametime, are sufficiently biodegradable in normal composting conditions andare therefore usable in applications in which such properties arerequired.

The polyester resins usable in the applications of the invention areformed by recurring units X=[O—(CH₂)_(n)—OCO—(CH₂)_(m)—CO] and/orY=[O—(CH₂)_(k)—CO], where the half-sum of n+m is equal to or greaterthan 6 and k is a number equal to or greater than 6, or by copolymerscomprising units and/or sequences having the formulax_(i)[O—(CH₂)_(ni)—OCO—(CH₂)_(mi)CO]; y_(j)[O—(CH₂)_(k)—CO] where:

i,j=1-5; n _(i)=2-22; m _(i)=0-20; k _(j)=1=21;

${\sum\limits_{i = 1}^{5}x_{i}} + {\sum\limits_{j = 1}^{5}y_{j}} + 1$

and x_(i) and y_(j) vary between 0 and 1 and are molar fractions of thevarious units such that${{{\sum\limits_{i = 1}^{5}{x_{i} \cdot ( \frac{n_{i} + m_{i}}{2} )}} + {\sum\limits_{j = 1}^{5}{y_{j} \cdot k_{j}}}} \geq 6},$

or by recurring units

Z=[O—(CH₂)_(a)—OCO—(CH₂)_(b)—CO] where a=2-3 and b=7-11, present insufficient quantity to ensure good barrier properties andbiodegradability of the resins in the production of products in which apermeability to water vapour of less than 350 g×30 μm/m² per day at 38°C. and 90% RH and biodegradability in composting or burial conditionsare required.

The products which can be produced from the polyesters as defined abovecan ensure permeability to water vapour of less than 350, moreparticularly less than 300, g×30 μm/m² per day at 38° C. and 90% RH.

The biodegradability of the products during composting or burial issufficient to bring about their decomposition within the requiredperiods of time.

More particularly, in the case of the products produced from thepreferred polyester resins, the biodegradability is less than 30% in onemonth and more than 60% in six months, in accordance with DIN 54900,part II, or decomposition on 30 μm film of less than 10% in 14 days andmore than 90% in 6 months, in accordance with the method described in“Journal of Environmental Polymer Degradation”, Vol. 4, No. 1, 1996, p.55-63, or in accordance with the burial test described in “BiodegradablePlastics, Practices and Test Methods” ASTM Subsection D-20.96.1 ofEnvironmental Degradable Plastics, Version 4.0 Dec. 6, 1990.

The polyester resins usable according to the invention have a meannumeral molecular weight greater than 10000 and a melting point(acceptable for industrial applications) of between 60 and 110° C.

Polyester resins with a mean numeral molecular weight of between 45000and 70000 have been found particularly advantageous for use according tothe invention.

There is not the slightest reference in the literature either to thebarrier properties, particularly to water vapour, of the polyesterresins falling within the general formula given above, or to their goodbiodegradability by decomposition.

The use of the above-mentioned polyester resins in applications whichrequire a low permeability to water vapour (below the value indicatedabove) combined with a biodegradability during composting compatiblewith the standards in use is novel and constitutes the subject of thepresent invention.

Examples of applications in which the polyester resins according to theinvention are particularly useful are:

coatings produced by extrusion-coating with good water-barrierproperties, particularly for the packaging of fresh milk and diaryproducts, of meat, and of foods with high water content,

multi-layer laminates with layers of paper, plastics material orpaper/plastics material, aluminium and metallized films in general,

films as such, and multi-layer films with other polymer materials,

sacks for organic refuse and for grass cuttings with periods of useLonger than 1 week,

single-layer and multi-layer food packaging, particularly containers formilk, yoghurt, cheeses, meat and beverages, in which the layer incontact with the food or beverage is formed by the polyester,

composites with gelatinized starch, destructured starch, native starchin the form of a filler, or complexed starch,

mono-directional or bi-directional films,

semi-expanded and expanded products produced by physical and/or chemicalmeans, by extrusion, injection, or agglomeration of pre-expandedparticles, from materials constituted by the polyester as such, fromblends, or from filled materials,

expanded sheet and expanded containers for foods, (fruit, vegetables,meat, cheeses) for drugs, and for fast-food,

fibres, fabrics and non-woven fabrics in the hygiene, sanitary andclothing fields,

outer non-woven fabric and/or film, front tapes for increasing thethickness of the backsheet in critical points, and adhesive strips, forthe production of nappies,

composites with mineral and vegetable fillers with various form ratios,

extruded or thermoformed sheets and profiles in the field of food andfast-food packaging (drinking straws, cups, trays, etc.),

bottles for the food, cosmetics and pharmaceutical fields,

fishing nets,

containers for fruit and vegetables,

irrigation pipes in the agricultural field,

products produced from blends with other biodegradable polymers (forexample, polybutylene succinate, polycaprolactone,polyhydroxybutyrate-co-valerate, polyesters-amides, aliphatic-aromaticpolyesters), for correcting the biodegradation rate, the processability,and/or the permeability to water of these latter polymers and thesuperficial properties such as migration phenomena of low molecularweight molecules,

products produced from blends with non-biodegradable polymers.

Polyesters falling within the general formula given above can beproduced by the polycondensation, in accordance with known methods, of abicarboxylic aliphatic acid with 2-22 carbon atoms with a diol with 2-22carbon atoms, selected in a manner such that the half-sum of the carbonatoms relating to the acid and to the diol, is equal to or, preferablygreater than 6, more preferably equal to 7, or by polycondensation ofhydroxy-acids with 7-22, preferably 8-22 carbon atoms, or byring-opening of the corresponding lactones or lactides; or bypolycondensation of ethylen glycol with azelaic and sebacic acid.

Aliphatic-aromatic copolyesters, aliphatic-polyamide copolyesters,aliphatic-ether copolyesters, aliphatic-urea copolyesters or linear orbranched urethanes in which the fraction of the aliphatic polyesters ofthe copolymers have the structure given above, and also blends of thesepolyester resins with unmodified or modified polysaccharides, withwater-vapour barrier properties of the type defined above, also fallwithin the scope of the invention.

Examples of bicarboxylic acids usable are succinic, adipic, pimelic,suberic, azelaic, sebacic, brassilic, undecandioic and dodecandioicacids, and dimeric acids; examples of hydroxy-acids which may be usedare glycolic, hydroxybutyric, hydroxypropionic, hydroxycaproic,hydroxyvaleric, 7-hyroxyheptanoic, 8-hydroxyoctanoic, 9-hydroxynonoic,10-hydroxydecanoic and 13-hydroxytridecancarboxylic acids.

Examples of diols which may be used are 1,2-ethandiol, 1,4-butandiol,1,6-hexandiol, 1,7-heptandiol, 1,8-octandiol, 1,9-nonandiol,1,10-decandiol, 1,12-dodecandiol, 1,4-cyclohexandimethylol and1,4-cyclohexandiol.

Diacids and dialcohols which come from renewable sources and which canbe produced from fatty acids such as oleic and ricinoleic acids arepreferred.

When the diol has less than 7 carbon atoms, the acid has a number ofcarbon atoms such that the half-sum of the carbon atoms of the diol andof the acid is equal to or greater than 6, more preferably equal orhigher than 7. The same criterion applies when the bicarboxylic acid hasless than 7 carbon atoms.

The polycondensation is performed at temperatures of between 180° and230° C. in the presence of known catalysts based on transition andrare-earth metals such as tin, titanium, antimony, zinc, etc.

In the case of copolymers formed by or containing units or sequences ofunits X and Y, the preparation is performed in accordance with knownmethods by polycondensation of the diacid and the diol in the presenceof the preselected lactone or lactide.

The mean numeral molecular weight obtainable by polycondensation may goup to values of the order of 100000 but it is preferably kept between45000 and 70000.

Mean numeral molecular weights of less than 10000 do not permit theproduction of products having mechanical properties of practicalinterest.

The molecular weight can be increased by post-condensation reactions,operating either in the fused state or in the solid state, in thepresence of polyfunctional compounds having groups reactive with theterminal —OH groups of the polyester, such as aliphatic or aromaticdiisocyanates.

For post-condensation reactions (upgrades) in the solid state, thereaction is carried out by placing the solid resin in granular form incontact with the polyfunctional compound at ambient temperature or at atemperature slightly below the melting point of the resin for a periodof time sufficient to bring about the desired increase in molecularweight.

The polyfunctional compound is used in the molten state, or dispersedhomogeneously on the solid resin. Preferably, however, it is mixed withthe resin in the fused state, for example, in an extruder, with periodsof less than 5 minutes spent in the extruder to prevent undesiredcross-linking reactions.

The intrinsic viscosity (measured in chloroform at 25° C.) is increasedeven beyond 1 dl/g. Preferably, it is brought to values greater than 0.7dl/g and most preferably between 0.8 and 2.5 dl/g. The viscosity of theresin in the fused state after upgrading is generally between 2000 and30000 Pas measured at 180° C. and with a “shear rate” of 100 sec⁻¹.

Diisocyanates are the preferred polyfunctional compounds acting as chainextenders; they are used in sufficient quantity to react with theterminal —OH groups of the resin. The quantity is between 0.2 and 1equivalent of —NCO isocyanic groups per —OH group of the resin.

The quantity, expressed by weight, is generally between 0.01 and 3% ofthe resin, preferably between 0.1 and 2%.

The preferred diisocyanates are hexamethylene diisocyanate,diphenylmethane diisocyanate and isophorone diisocyanate.

Examples of other polyfunctional compounds which may be used areepoxides such as epoxy ethane, and the dianhydrides of tetracarboxylicaromatic acids such as pyromellitic anhydride.

The dianhydrides and the epoxides are also generally used in quantitiesof between 0.01 and 2% by weight of the resin.

The following examples are provided by way of non-limiting illustrationof the invention.

EXAMPLE 1

A polybutylene sebacate film having an intrinsic viscosity of 1.26measured at 0.2 g/dl in chloroform at 25° C. (produced bypolycondensation of sebacic acid with 1,4-butandiol) was used for theproduction of organic refuse sacks, bags for growing plants ingreenhouses with metering of micro-nutrients, mulching films, bags forvegetables and tubers which do not sweat, or for other specificapplications in which a low permeability to water vapour is required.The permeability to water vapour of this film was 250 g×30 μm/m² per dayat 38° C. and 90% RH.

The film for the different applications has been produced using aGhioldi machine for film-blowing of 40 mm of diameter and L/D=30, atemperature of 125 C. and 60 rpm. The head of 100 mm was cooled with airat 10 C.

The polymer was also found particularly suitable for the production ofproducts which are to come into contact with liquid foods, such asthermoformed cups, drinking straws and plates for fast-food.

In case of thermoformed sheets the sheets have been produced with a monoscrew extruder of 30 mm of diameter and L/D=30, using a flat head of 20cm of width. The extrusion temperature was of 13 ° C., the thickness wasof 700 microns. The sheet has been thermoformed at 80 C. in a round cup.In case of drinking straws a MAI machine was used of 60 mm of diameterand L/D=25. The productivity at 150 C. was comparable with the one ofpolyethylene.

EXAMPLE 2

A polyhexamethylene sebacate film having an intrinsic viscosity of 0.7dl/g (produced by polycondensation of sebacic acid with 1,6-hexandioland subsequent upgrading with 1,6-hexamethylene diisocyanate at 60° C.to give an intrinsic viscosity of 1.3 dl/g) was used for the productionof organic refuse sacks, bags for growing plants in greenhouses withmetering of micro-nutrients, mulching films, bags for vegetables andtubers which do not sweat, or for other specific applications in which alow permeability to water vapour is required as in example 1.

The permeability to water vapour of this film was 180 g×30 μm/m² per dayat 38° C. and 90% RH.

EXAMPLE 3

Polyhexamethylene sebacate having an intrinsic viscosity of 1.3 dl/g wasused for the production of single-layer and multi-layer films and sheetsand for the production of containers for foods and drinks. An HAAKERHEOCORD machine was used with a diameter of 19 mm and L/D=25. The flathead had a width of 10 cm. The molten film was calandered on cardboardin order to obtain an extrusion coated product for food containers.

COMPARISON EXAMPLE 1

Polyhexamethylene adipate was used for the production of films thepermeability of which was 700 g×30 μm/m² per day at 38° C. and 90% RH.

EXAMPLE 4

The barrier properties of the following polymers were measured: polyethylene sebacate poly nonandiol sebacate, poly decandiol sebacate,polyoctandiol azelate, polyoctandiol brassilate.

The barrier properties, expressed as permeability to vapour in g×30μm/m² per day (measured with a Lissy L80-4000 vapour permeability testerat 38° C. and 90% RH) were 300, 109, 100, 168, and 98, respectively.

The biodegradation behaviour according to the method described in“Journal of Environmental Polymer Degradation” vol. 4, N1, 1996, p55-63for all the polymers fell inside the range of less than 10% ofbiodegradation in 14 days and more than 90% in 6 months.

We claim:
 1. A method of making a biodegradable article having apermeability to water vapor of less than 350 g×30 μm/m² per day at 38°C. and 90% RH comprising: manufacturing articles from aliphaticpolyester resin, wherein said aliphatic polyester resin furthercomprises a) recurring units X=[O—(CH₂)_(n)—OCO—(CH₂)_(m)—CO] and/orY=[O—(CH₂)_(k)—CO], where the half-sum of n+m is equal to or greaterthan 6 and k is a number equal to or greater than 6, or by copolymerscomprising units and/or sequences having the formulax_(i)[O—(CH₂)_(ni)—OCO—(CH₂)_(mi)—CO]; y_(j)[O—(CH₂)_(kj)—CO] where: i,j=1-5; n_(i)=2-22; m_(i)=0-20; k_(j)=1-21;${{\sum\limits_{i = 1}^{5}x_{i}} + {\sum\limits_{j = 1}^{5}y_{j}}} = 1$

and x_(i) and y_(j) vary between 0 and 1 and are molar fractions of thevarious units such that${{{\sum\limits_{i = 1}^{5}{x_{i} \cdot ( \frac{n_{i} + m_{i}}{2} )}} + {\sum\limits_{j = 1}^{5}{y_{j} \cdot k_{j}}}} \geq 6},$

or b) recurring units Z=[O—(CH₂)a-OCO—(CH₂)b-CO] where a=2-3, b=7-11,and has an intrinsic viscosity (in chloroform at 25° C.) greater than0.7 and up to 2.5 dl/g, a melting point from 60° to 110° C., and abiodegradability such that, under composting conditions, a 30 μm film ofsaid resin shows a decomposition of less than 10% in 14 days and morethan 90% in six months.
 2. The method of claim 1, in which the polyesterresin is produced by polycondensation of bicarboxylic aliphatic acidswith from 2 to 22 carbon atoms and of diols with from 2 to 22 carbonatoms, selected in a manner such that the half-sum of the number ofcarbon atoms relating to the acid and to the diol is greater than 6, orby polycondensation of hydroxyl-acids, or by ring-opening ofcorresponding lactones or lactides having 7 to 22 carbon atoms.
 3. Themethod of claim 2, in which the diacids and the dialcohols are obtainedfrom renewable resources.
 4. The method of claim 1, in which thepolyester resin is selected from polyethylene sebacate, polybutandiolsebacate, polyhexandiol azelate, polyhexandiol sebacate, polynonandiolazelate, polynonandiol sebacate, polyoctandiol azelate, polyocatandiolbrassilate, polydecandiol sebacate, and polydecandiol brassilate.
 5. Themethod of claim 1, in which the polyester resin is subjected to anupgrading process.
 6. The method of claim 1, in which the polyesterresin is a component of a blend of unmodified or modifiedpolysacchanides.
 7. The method of claim 1, in which the polyester resincontains mineral or vegetable fillers and/or additives selected fromlubricants, plasticizers, colourings, flavourings, perfumes,flame-proofing agents, stabilizers with regard to hydrolysis and tothermal degradation, and antioxidants.
 8. The method of claim 1, inwhich the mean numeral molecular weight of the polyester resin isbetween 45000 and
 70000. 9. The method of claim 1, wherein said articlesare selected from: coatings which are produced by extrusion-coating,with water-vapour barrier properties, and which are usable for thepackaging of fresh milk and dairy products, of meat, and of foods havinghigh water content, multilayer laminates with layers of paper, plasticsmaterial and or paper/plastics material, aluminum and metalized films,films as such and multi-layer films with other polymer materials, sacksfor organic refuse and for grass cuttings with periods of use longerthan 1 week, single-layer and multi-layer food packaging comprisingcontainers for milk, toghurt, cheeses, meat and beverages, in which thelayer in contact with the food or beverage is formed by the aliphaticpolyester, composites with gelatinized or destructured starch, and/orcomplexed starch or natural starch as a filler, mono-directional andbi-directional films, semi-expanded and expanded products produced byphysical and/or chemical means, by extrusion, injection, oragglomeration or pre-expanded particles, expanded sheet and expandedcontainers for foods, for drugs, and for fast food, fibres, fabrics andnon-woven fabrics in the hygiene, sanitary, and clothing fields,composites with mineral and vegetable fillers thermoformed sheets forthe food or fast-food packaging fields, bottles for the food cosmeticsand pharmaceutical fields, fishing nets, containers for fruit andvegetables, extruded sections usable in the fast-food field andirrigation pipes in the agricultural field.
 10. Polyester resins asdefined in claim 1 in blends with other biodegradable polymers having apermeability to water vapour greater than 300 g×30 μm/m² per day at 38°C. and 90% RH.
 11. Polyester resins as defined in claim 1 in blends withpolylactic acid.
 12. Polyester resins as defined in claim 1 in blendswith other non-biodegradable polymers, the said polymers having apermeability to water vapour greater than 300 g×30 μm/m² per day at 38°C. and 90% RH.
 13. An article of manufacture comprising: a biodegradablearticle having a permeability to water vapor of less than 350 g×30 μm/m²per day at 38° C. and 90% RH manufactured from aliphatic polyesterresin,  wherein said aliphatic polyester resin further comprises a)recurring units X=[O—(CH₂)_(n)—OCO—(CH₂)_(m)—CO] and/orY=[O—(CH₂)_(k)—CO], where the half-sum of n+m is equal to or greaterthan 6 and k is a number equal to or greater than 6, or by copolymerscomprising units and/or sequences having the formulax_(i)[O—(CH₂)_(ni)—OCO—(CH₂)_(mi)—CO]; y_(j)[O—(CH₂)_(kj)—CO] where: i,j=1-5; n_(i)=2-22; m_(i)=0-20; k_(j)=1-21;${{\sum\limits_{i = 1}^{5}x_{i}} + {\sum\limits_{j = 1}^{5}y_{j}}} = 1$

and x_(i) and y_(j) vary between 0 an 1 and are molar fractions of thevarious units such that${{{\sum\limits_{i = 1}^{5}{x_{i} \cdot ( \frac{n_{i} + m_{i}}{2} )}} + {\sum\limits_{j = 1}^{5}{y_{j} \cdot k_{j}}}} \geq 6},$

or b) recurring units Z=[O—(CH₂)a-OCO—(CH₂)b-CO] where a=2-3, b=7-11,and has an intrinsic viscosity (in chloroform at 25° C.) greater than0.7 and up to 2.5 dl/g, a melting point from 60° to 110° C., and abiodegradability such that, under composting conditions, a 30 μm film ofsaid resin shows a decomposition of less than 10% in 14 days and morethan 90% in six months.